With the advancement of digital techniques, images are increasingly processed as digital data (image data). Imaging devices such as digital cameras enable immediate output of captured images in the form of image data. Imaging devices are typically equipped with an electronic image sensor consisting of small elements for converting light intensities into electric signals. The imaging device focuses a captured image of a subject on the image sensor by means of an optical system and detects the light intensities in the individual elements as electric signals to generate image data. The light entering the optical system may be divided into three color components, R, G, and B corresponding to three primary colors of light. The respective color lights of the three color components R, G, and B are directed to the image sensor, and the electric signals representing the light intensities of the respective color components acquired by the sensor are output to generate color image data. It is noted that G components are often referred to as “luminance” components whereas R and B components are often referred to as “chrominance” components.
The simplest method of acquiring the respective color lights of the three color components R, G, and B (which are obtained as divisions of the light entering the optical system) by the image sensor uses a spectroscopic prism to divide the incident light into the color lights of the three color components R, G, and B and focuses the respective color lights on image sensors to generate image data with regard to the respective color components R, G, and B. This method undesirably requires the three image sensors. Therefore, an imaging device relying on three image sensors to capture color images is sometimes called a “three image sensor” device. To reduce the cost of an imaging device, one common technique uses a color filter array to allocate one of the R, G, and B color components to each of the light-sensitive elements constituting the image sensor in order to attain detection of the respective color components R, G, and B by a single image sensor. A typical configuration of this technique provides small color filters allowing transmission of only the R component in front of the photo-elements assigned for detection of the R component, small color filters allowing transmission of only the G component in front of the elements assigned for detection of the G component, and small color filters allowing transmission of only the B component in front of the elements assigned for detection of the B component. Since each element assigned for detection of a predetermined color component (for example, the R component) is unable to detect the other color components (for example, the G component and the B component), the resulting image data accordingly has a mosaic arrangement of pixels of the R component, pixels of the G component, and pixels of the B component in order to allow effective restoration of two color components in each pixel location. Interpolation of these two missing color components in each pixel with color components of adjacent pixels enables generation of color image data with the settings of all the color components R, G, and B in all the pixels.
The process of interpolating the missing color components in the image data of the mosaic arrangement to generate color image data with the settings of all the color components R, G, and B is sometimes referred to as “demosaicing process”. An imaging device that uses only one image sensor covered by a color filter array is occasionally called a “single image sensor” device.
The single image sensor device requires the interpolation of the missing color components. This naturally consumes the time for interpolation and may cause the occurrence of aliasing colors due to interpolation error. There are diverse proposed techniques with a view to preventing the occurrence of aliasing colors while minimizing an increase of the time required for interpolation. One proposed technique computes color difference components (for example, differences between the G component and the R component) in the respective pixels after computation of the missing color components, removes the pixel with the maximum color difference component and the pixel with the minimum color difference component as noise from a pixel array of a preset number of pixels including a target pixel, and recalculates the respective color components in the target pixel (see JP-A-2005-167974). Another proposed technique applies low-pass filters to the color difference components computed in the respective pixels and recalculates the respective color components in the target pixel from the color difference components after removal of noise (see JP-A-2005-260908).
With the consumers' increasing demands for the higher picture quality of imaging devices, development of a demosaicing technique that prevents the occurrence of aliasing colors has been highly demanded. The number of pixels constituting each image captured by the imaging device is increasing to fulfill the consumers' demands for the higher picture quality. Development of a demosaicing technique that enables the high-speed processing thus has also been demanded.